In recent years, services of carrying out video communications on an IP network in real time, such as video delivery, have become widespread. Because an IP network is a best-effort network and does not guarantee network transmission quality, a transfer delay may occur in a packet and packet losses may occur. In addition, also in a video receiving terminal which receives services, packet discarding due to a buffer overflow or the like may occur. To solve this problem, there is a necessity to provide a technique of, if the quality of a video which a user is watching and listening deteriorates when providing a video communication service, isolating the cause of the deterioration.
As the technique of isolating the cause of a quality deterioration, there is a method of, when a deterioration has occurred, determining whether the deterioration has occurred in either one of an external network side which is a network outside the user's house, a home network side which is a network in the user's house, and the video receiving terminal.
As the technique of isolating the cause of a quality deterioration, there is a method as disclosed in, for example, patent reference 1. According to this method, quality information of a video stream is measured in a relay device, such as a home gateway device, between an external network and a home network, and a video receiving terminal. Information about packet losses and packet delays are included in the quality information. By comparing the quality information measured in the relay device with that measure in the video receiving terminal, whether the cause of a quality deterioration is in the external network side, the home network side or the video receiving terminal can be determined and notified.